And because it isn't always necessary to recap a plot from a Marx Bros. film (particularly those made at Paramount), I'm just going to lead with the scene in question and work backwards to the story from there:

The mirror gag occurs in one of the few moments Harpo and Chico are behaving like the spies they ostensibly are. Chicolini (Chico) and Pinky (Harpo) have been hired by Trentino (Louis Calhern) the ambassador of Sylvania, a vaguely Balkan-looking country, to dig up political or personal weaknesses in Rufus T. Firefly (Groucho), the newly-elected president of Freedonia, a rival nation that looks slightly less Balkan. Trentino would like to annex the country for Sylvania. The reason everyone is in their nightshirts in this scene is that Firefly is guarding Freedonia's plans for the upcoming war, which are hidden in the safe at the home of his benefactress, Mrs. Teasdale (Margaret Dumont, the greatest unwitting sport in the history of film).Both Harpo and Chico have dressed themselves up like Groucho to fool Mrs. Teasdale into giving them the combination to the safe. At one point, Harpo has broken a full-length mirror just as Groucho rounds the corner, and the rest, as they say, is plot-incidental history.

Timely Aside: Here are Max Linder and an uncredited actor as his cook performing the exact same gag to set up what is a pivotal plot point in Seven Years Bad Luck (1921), which I saw for the first time yesterday.

President Firefly appoints Chicolini and Pinky to his cabinet knowing full well they are spies for Trentino, but it doesn't matter in the slightest. Firefly barely has allegiance to his own country and is, in fact, directly responsible for the war that rages between Freedonia and Sylvania.

There are a number of classic bits in Duck Soup: The clash between burly lemonade vendor Edgar Kennedy (a Keystone comedy veteran) and spies/peanut vendors Chicolini and Pinky; the running gag of the sidecar; great lines like "Remember, you're fighting for this woman's honor, which is probably more than she ever did."

But the best of all is the crazy-ass musical number sung by the entire cast about the thrill of going to war. Every opinion is represented and overtaken (or overruled) by the jubilation ("all god's chillun got guhh-uns!") with the four brothers playing and singing and pranking the lot. When the war is on in full, each cutaway to Firefly puts him in a different uniform. First he's Union, then Confederate, then Davy Crockett, then a scoutmaster. They're outnumbered, outgunned, and shells are sailing through the windows (until Firefly draws the blind). Chicolini and Pinky have switched sides a bunch of times and even Mrs. Teasdale shoulders a rifle during the final stand-off, which they, of course, and against all odds, emerge victorious.

See? Pointless. Like political backbiting between and within governments? Like war? It's tempting to ascribe a method to Duck Soup's madness, but I'm inclined to resist. Those guys were crazy funny geniuses, but their routines are hardscrabble, 20th-century American satyr plays that satirized everything by ridicule, not necessary for social commentary. That said, I think Duck Soup ranks as one of the best anti-war movies ever, just as Horse Feathers is a pretty sharp indictment of how sports can bulldoze over academics at institutions of higher learning. For that perspective, we probably need to thank scenarist, Arthur Sheekman, who wrote many of the Marx's movies.Duck Soup was to be the last film the four Marx Brothers would make at Paramount and the last they'd all four make together. Zeppo (Herbert Marx), who had been kind of a straight man (I always thought he was very funny) and romantic lead (which he was; see torn shirt below) went on to become a theatrical agent and inventor. He was the most mechanically-inclined of the brothers and ran a machine shop that manufactured (among other things) the Marman clamps that held the "fat man" A-Bomb securely in place inside the B-29 bomber. A regular Hedy Lamarr (I refer you again to the photo below).

See Duck Soup again if you haven't in a long while. It's only about an hour and 15 minutes, so your kids can watch it too. Come for the spies, stay for the crazy.

Zeppo (2nd from left) in a torn undershirt. These boys knew their business.